/*
 * Copyright (c) 2013, 2015, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */
package java.lang;

import java.io.InputStream;
import java.io.IOException;
import java.io.File;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.net.MalformedURLException;
import java.net.URL;
import java.security.AccessController;
import java.security.AccessControlContext;
import java.security.CodeSource;
import java.security.Policy;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.security.ProtectionDomain;
import java.security.cert.Certificate;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Set;
import java.util.Stack;
import java.util.Map;
import java.util.Vector;
import java.util.Hashtable;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentHashMap;
import sun.misc.CompoundEnumeration;
import sun.misc.Resource;
import sun.misc.URLClassPath;
import sun.misc.VM;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;
import sun.reflect.misc.ReflectUtil;
import sun.security.util.SecurityConstants;

/**
 * A class loader is an object that is responsible for loading classes. The
 * class <tt>ClassLoader</tt> is an abstract class.  Given the <a
 * href="#name">binary name</a> of a class, a class loader should attempt to
 * locate or generate data that constitutes a definition for the class.  A
 * typical strategy is to transform the name into a file name and then read a
 * "class file" of that name from a file system.
 *
 * <p> Every {@link Class <tt>Class</tt>} object contains a {@link
 * Class#getClassLoader() reference} to the <tt>ClassLoader</tt> that defined
 * it.
 *
 * <p> <tt>Class</tt> objects for array classes are not created by class
 * loaders, but are created automatically as required by the Java runtime.
 * The class loader for an array class, as returned by {@link
 * Class#getClassLoader()} is the same as the class loader for its element
 * type; if the element type is a primitive type, then the array class has no
 * class loader.
 *
 * <p> Applications implement subclasses of <tt>ClassLoader</tt> in order to
 * extend the manner in which the Java virtual machine dynamically loads
 * classes.
 *
 * <p> Class loaders may typically be used by security managers to indicate
 * security domains.
 *
 * <p> The <tt>ClassLoader</tt> class uses a delegation model to search for
 * classes and resources.  Each instance of <tt>ClassLoader</tt> has an
 * associated parent class loader.  When requested to find a class or
 * resource, a <tt>ClassLoader</tt> instance will delegate the search for the
 * class or resource to its parent class loader before attempting to find the
 * class or resource itself.  The virtual machine's built-in class loader,
 * called the "bootstrap class loader", does not itself have a parent but may
 * serve as the parent of a <tt>ClassLoader</tt> instance.
 *
 * <p> Class loaders that support concurrent loading of classes are known as
 * <em>parallel capable</em> class loaders and are required to register
 * themselves at their class initialization time by invoking the
 * {@link
 * #registerAsParallelCapable <tt>ClassLoader.registerAsParallelCapable</tt>}
 * method. Note that the <tt>ClassLoader</tt> class is registered as parallel
 * capable by default. However, its subclasses still need to register themselves
 * if they are parallel capable. <br>
 * In environments in which the delegation model is not strictly
 * hierarchical, class loaders need to be parallel capable, otherwise class
 * loading can lead to deadlocks because the loader lock is held for the
 * duration of the class loading process (see {@link #loadClass
 * <tt>loadClass</tt>} methods).
 *
 * <p> Normally, the Java virtual machine loads classes from the local file
 * system in a platform-dependent manner.  For example, on UNIX systems, the
 * virtual machine loads classes from the directory defined by the
 * <tt>CLASSPATH</tt> environment variable.
 *
 * <p> However, some classes may not originate from a file; they may originate
 * from other sources, such as the network, or they could be constructed by an
 * application.  The method {@link #defineClass(String, byte[], int, int)
 * <tt>defineClass</tt>} converts an array of bytes into an instance of class
 * <tt>Class</tt>. Instances of this newly defined class can be created using
 * {@link Class#newInstance <tt>Class.newInstance</tt>}.
 *
 * <p> The methods and constructors of objects created by a class loader may
 * reference other classes.  To determine the class(es) referred to, the Java
 * virtual machine invokes the {@link #loadClass <tt>loadClass</tt>} method of
 * the class loader that originally created the class.
 *
 * <p> For example, an application could create a network class loader to
 * download class files from a server.  Sample code might look like:
 *
 * <blockquote><pre>
 *   ClassLoader loader&nbsp;= new NetworkClassLoader(host,&nbsp;port);
 *   Object main&nbsp;= loader.loadClass("Main", true).newInstance();
 *       &nbsp;.&nbsp;.&nbsp;.
 * </pre></blockquote>
 *
 * <p> The network class loader subclass must define the methods {@link
 * #findClass <tt>findClass</tt>} and <tt>loadClassData</tt> to load a class
 * from the network.  Once it has downloaded the bytes that make up the class,
 * it should use the method {@link #defineClass <tt>defineClass</tt>} to
 * create a class instance.  A sample implementation is:
 *
 * <blockquote><pre>
 *     class NetworkClassLoader extends ClassLoader {
 *         String host;
 *         int port;
 *
 *         public Class findClass(String name) {
 *             byte[] b = loadClassData(name);
 *             return defineClass(name, b, 0, b.length);
 *         }
 *
 *         private byte[] loadClassData(String name) {
 *             // load the class data from the connection
 *             &nbsp;.&nbsp;.&nbsp;.
 *         }
 *     }
 * </pre></blockquote>
 *
 * <h3> <a name="name">Binary names</a> </h3>
 *
 * <p> Any class name provided as a {@link String} parameter to methods in
 * <tt>ClassLoader</tt> must be a binary name as defined by
 * <cite>The Java&trade; Language Specification</cite>.
 *
 * <p> Examples of valid class names include:
 * <blockquote><pre>
 *   "java.lang.String"
 *   "javax.swing.JSpinner$DefaultEditor"
 *   "java.security.KeyStore$Builder$FileBuilder$1"
 *   "java.net.URLClassLoader$3$1"
 * </pre></blockquote>
 *
 * @see #resolveClass(Class)
 * @since 1.0
 */
public abstract class ClassLoader {

  private static native void registerNatives();

  static {
    registerNatives();
  }

  // The parent class loader for delegation
  // Note: VM hardcoded the offset of this field, thus all new fields
  // must be added *after* it.
  private final ClassLoader parent;

  /**
   * Encapsulates the set of parallel capable loader types.
   */
  private static class ParallelLoaders {

    private ParallelLoaders() {
    }

    // the set of parallel capable loader types
    private static final Set<Class<? extends ClassLoader>> loaderTypes =
        Collections.newSetFromMap(
            new WeakHashMap<Class<? extends ClassLoader>, Boolean>());

    static {
      synchronized (loaderTypes) {
        loaderTypes.add(ClassLoader.class);
      }
    }

    /**
     * Registers the given class loader type as parallel capabale.
     * Returns {@code true} is successfully registered; {@code false} if
     * loader's super class is not registered.
     */
    static boolean register(Class<? extends ClassLoader> c) {
      synchronized (loaderTypes) {
        if (loaderTypes.contains(c.getSuperclass())) {
          // register the class loader as parallel capable
          // if and only if all of its super classes are.
          // Note: given current classloading sequence, if
          // the immediate super class is parallel capable,
          // all the super classes higher up must be too.
          loaderTypes.add(c);
          return true;
        } else {
          return false;
        }
      }
    }

    /**
     * Returns {@code true} if the given class loader type is
     * registered as parallel capable.
     */
    static boolean isRegistered(Class<? extends ClassLoader> c) {
      synchronized (loaderTypes) {
        return loaderTypes.contains(c);
      }
    }
  }

  // Maps class name to the corresponding lock object when the current
  // class loader is parallel capable.
  // Note: VM also uses this field to decide if the current class loader
  // is parallel capable and the appropriate lock object for class loading.
  private final ConcurrentHashMap<String, Object> parallelLockMap;

  // Hashtable that maps packages to certs
  private final Map<String, Certificate[]> package2certs;

  // Shared among all packages with unsigned classes
  private static final Certificate[] nocerts = new Certificate[0];

  // The classes loaded by this class loader. The only purpose of this table
  // is to keep the classes from being GC'ed until the loader is GC'ed.
  private final Vector<Class<?>> classes = new Vector<>();

  // The "default" domain. Set as the default ProtectionDomain on newly
  // created classes.
  private final ProtectionDomain defaultDomain =
      new ProtectionDomain(new CodeSource(null, (Certificate[]) null),
          null, this, null);

  // The initiating protection domains for all classes loaded by this loader
  private final Set<ProtectionDomain> domains;

  // Invoked by the VM to record every loaded class with this loader.
  void addClass(Class<?> c) {
    classes.addElement(c);
  }

  // The packages defined in this class loader.  Each package name is mapped
  // to its corresponding Package object.
  // @GuardedBy("itself")
  private final HashMap<String, Package> packages = new HashMap<>();

  private static Void checkCreateClassLoader() {
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
      security.checkCreateClassLoader();
    }
    return null;
  }

  private ClassLoader(Void unused, ClassLoader parent) {
    this.parent = parent;
    if (ParallelLoaders.isRegistered(this.getClass())) {
      parallelLockMap = new ConcurrentHashMap<>();
      package2certs = new ConcurrentHashMap<>();
      domains =
          Collections.synchronizedSet(new HashSet<ProtectionDomain>());
      assertionLock = new Object();
    } else {
      // no finer-grained lock; lock on the classloader instance
      parallelLockMap = null;
      package2certs = new Hashtable<>();
      domains = new HashSet<>();
      assertionLock = this;
    }
  }

  /**
   * Creates a new class loader using the specified parent class loader for
   * delegation.
   *
   * <p> If there is a security manager, its {@link
   * SecurityManager#checkCreateClassLoader()
   * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
   * a security exception.  </p>
   *
   * @param parent The parent class loader
   * @throws SecurityException If a security manager exists and its <tt>checkCreateClassLoader</tt>
   * method doesn't allow creation of a new class loader.
   * @since 1.2
   */
  protected ClassLoader(ClassLoader parent) {
    this(checkCreateClassLoader(), parent);
  }

  /**
   * Creates a new class loader using the <tt>ClassLoader</tt> returned by
   * the method {@link #getSystemClassLoader()
   * <tt>getSystemClassLoader()</tt>} as the parent class loader.
   *
   * <p> If there is a security manager, its {@link
   * SecurityManager#checkCreateClassLoader()
   * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
   * a security exception.  </p>
   *
   * @throws SecurityException If a security manager exists and its <tt>checkCreateClassLoader</tt>
   * method doesn't allow creation of a new class loader.
   */
  protected ClassLoader() {
    this(checkCreateClassLoader(), getSystemClassLoader());
  }

  // -- Class --

  /**
   * Loads the class with the specified <a href="#name">binary name</a>.
   * This method searches for classes in the same manner as the {@link
   * #loadClass(String, boolean)} method.  It is invoked by the Java virtual
   * machine to resolve class references.  Invoking this method is equivalent
   * to invoking {@link #loadClass(String, boolean) <tt>loadClass(name,
   * false)</tt>}.
   *
   * @param name The <a href="#name">binary name</a> of the class
   * @return The resulting <tt>Class</tt> object
   * @throws ClassNotFoundException If the class was not found
   */
  public Class<?> loadClass(String name) throws ClassNotFoundException {
    return loadClass(name, false);
  }

  /**
   * Loads the class with the specified <a href="#name">binary name</a>.  The
   * default implementation of this method searches for classes in the
   * following order:
   *
   * <ol>
   *
   * <li><p> Invoke {@link #findLoadedClass(String)} to check if the class
   * has already been loaded.  </p></li>
   *
   * <li><p> Invoke the {@link #loadClass(String) <tt>loadClass</tt>} method
   * on the parent class loader.  If the parent is <tt>null</tt> the class
   * loader built-in to the virtual machine is used, instead.  </p></li>
   *
   * <li><p> Invoke the {@link #findClass(String)} method to find the
   * class.  </p></li>
   *
   * </ol>
   *
   * <p> If the class was found using the above steps, and the
   * <tt>resolve</tt> flag is true, this method will then invoke the {@link
   * #resolveClass(Class)} method on the resulting <tt>Class</tt> object.
   *
   * <p> Subclasses of <tt>ClassLoader</tt> are encouraged to override {@link
   * #findClass(String)}, rather than this method.  </p>
   *
   * <p> Unless overridden, this method synchronizes on the result of
   * {@link #getClassLoadingLock <tt>getClassLoadingLock</tt>} method
   * during the entire class loading process.
   *
   * @param name The <a href="#name">binary name</a> of the class
   * @param resolve If <tt>true</tt> then resolve the class
   * @return The resulting <tt>Class</tt> object
   * @throws ClassNotFoundException If the class could not be found
   */
  protected Class<?> loadClass(String name, boolean resolve)
      throws ClassNotFoundException {
    synchronized (getClassLoadingLock(name)) {
      // First, check if the class has already been loaded
      Class<?> c = findLoadedClass(name);
      if (c == null) {
        long t0 = System.nanoTime();
        try {
          if (parent != null) {
            c = parent.loadClass(name, false);
          } else {
            c = findBootstrapClassOrNull(name);
          }
        } catch (ClassNotFoundException e) {
          // ClassNotFoundException thrown if class not found
          // from the non-null parent class loader
        }

        if (c == null) {
          // If still not found, then invoke findClass in order
          // to find the class.
          long t1 = System.nanoTime();
          c = findClass(name);

          // this is the defining class loader; record the stats
          sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
          sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
          sun.misc.PerfCounter.getFindClasses().increment();
        }
      }
      if (resolve) {
        resolveClass(c);
      }
      return c;
    }
  }

  /**
   * Returns the lock object for class loading operations.
   * For backward compatibility, the default implementation of this method
   * behaves as follows. If this ClassLoader object is registered as
   * parallel capable, the method returns a dedicated object associated
   * with the specified class name. Otherwise, the method returns this
   * ClassLoader object.
   *
   * @param className The name of the to-be-loaded class
   * @return the lock for class loading operations
   * @throws NullPointerException If registered as parallel capable and <tt>className</tt> is null
   * @see #loadClass(String, boolean)
   * @since 1.7
   */
  protected Object getClassLoadingLock(String className) {
    Object lock = this;
    if (parallelLockMap != null) {
      Object newLock = new Object();
      lock = parallelLockMap.putIfAbsent(className, newLock);
      if (lock == null) {
        lock = newLock;
      }
    }
    return lock;
  }

  // This method is invoked by the virtual machine to load a class.
  private Class<?> loadClassInternal(String name)
      throws ClassNotFoundException {
    // For backward compatibility, explicitly lock on 'this' when
    // the current class loader is not parallel capable.
    if (parallelLockMap == null) {
      synchronized (this) {
        return loadClass(name);
      }
    } else {
      return loadClass(name);
    }
  }

  // Invoked by the VM after loading class with this loader.
  private void checkPackageAccess(Class<?> cls, ProtectionDomain pd) {
    final SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
      if (ReflectUtil.isNonPublicProxyClass(cls)) {
        for (Class<?> intf : cls.getInterfaces()) {
          checkPackageAccess(intf, pd);
        }
        return;
      }

      final String name = cls.getName();
      final int i = name.lastIndexOf('.');
      if (i != -1) {
        AccessController.doPrivileged(new PrivilegedAction<Void>() {
          public Void run() {
            sm.checkPackageAccess(name.substring(0, i));
            return null;
          }
        }, new AccessControlContext(new ProtectionDomain[]{pd}));
      }
    }
    domains.add(pd);
  }

  /**
   * Finds the class with the specified <a href="#name">binary name</a>.
   * This method should be overridden by class loader implementations that
   * follow the delegation model for loading classes, and will be invoked by
   * the {@link #loadClass <tt>loadClass</tt>} method after checking the
   * parent class loader for the requested class.  The default implementation
   * throws a <tt>ClassNotFoundException</tt>.
   *
   * @param name The <a href="#name">binary name</a> of the class
   * @return The resulting <tt>Class</tt> object
   * @throws ClassNotFoundException If the class could not be found
   * @since 1.2
   */
  protected Class<?> findClass(String name) throws ClassNotFoundException {
    throw new ClassNotFoundException(name);
  }

  /**
   * Converts an array of bytes into an instance of class <tt>Class</tt>.
   * Before the <tt>Class</tt> can be used it must be resolved.  This method
   * is deprecated in favor of the version that takes a <a
   * href="#name">binary name</a> as its first argument, and is more secure.
   *
   * @param b The bytes that make up the class data.  The bytes in positions <tt>off</tt> through
   * <tt>off+len-1</tt> should have the format of a valid class file as defined by <cite>The
   * Java&trade; Virtual Machine Specification</cite>.
   * @param off The start offset in <tt>b</tt> of the class data
   * @param len The length of the class data
   * @return The <tt>Class</tt> object that was created from the specified class data
   * @throws ClassFormatError If the data did not contain a valid class
   * @throws IndexOutOfBoundsException If either <tt>off</tt> or <tt>len</tt> is negative, or if
   * <tt>off+len</tt> is greater than <tt>b.length</tt>.
   * @throws SecurityException If an attempt is made to add this class to a package that contains
   * classes that were signed by a different set of certificates than this class, or if an attempt
   * is made to define a class in a package with a fully-qualified name that starts with "{@code
   * java.}".
   * @see #loadClass(String, boolean)
   * @see #resolveClass(Class)
   * @deprecated Replaced by {@link #defineClass(String, byte[], int, int) defineClass(String,
   * byte[], int, int)}
   */
  @Deprecated
  protected final Class<?> defineClass(byte[] b, int off, int len)
      throws ClassFormatError {
    return defineClass(null, b, off, len, null);
  }

  /**
   * Converts an array of bytes into an instance of class <tt>Class</tt>.
   * Before the <tt>Class</tt> can be used it must be resolved.
   *
   * <p> This method assigns a default {@link java.security.ProtectionDomain
   * <tt>ProtectionDomain</tt>} to the newly defined class.  The
   * <tt>ProtectionDomain</tt> is effectively granted the same set of
   * permissions returned when {@link
   * java.security.Policy#getPermissions(java.security.CodeSource)
   * <tt>Policy.getPolicy().getPermissions(new CodeSource(null, null))</tt>}
   * is invoked.  The default domain is created on the first invocation of
   * {@link #defineClass(String, byte[], int, int) <tt>defineClass</tt>},
   * and re-used on subsequent invocations.
   *
   * <p> To assign a specific <tt>ProtectionDomain</tt> to the class, use
   * the {@link #defineClass(String, byte[], int, int,
   * java.security.ProtectionDomain) <tt>defineClass</tt>} method that takes a
   * <tt>ProtectionDomain</tt> as one of its arguments.  </p>
   *
   * @param name The expected <a href="#name">binary name</a> of the class, or <tt>null</tt> if not
   * known
   * @param b The bytes that make up the class data.  The bytes in positions <tt>off</tt> through
   * <tt>off+len-1</tt> should have the format of a valid class file as defined by <cite>The
   * Java&trade; Virtual Machine Specification</cite>.
   * @param off The start offset in <tt>b</tt> of the class data
   * @param len The length of the class data
   * @return The <tt>Class</tt> object that was created from the specified class data.
   * @throws ClassFormatError If the data did not contain a valid class
   * @throws IndexOutOfBoundsException If either <tt>off</tt> or <tt>len</tt> is negative, or if
   * <tt>off+len</tt> is greater than <tt>b.length</tt>.
   * @throws SecurityException If an attempt is made to add this class to a package that contains
   * classes that were signed by a different set of certificates than this class (which is
   * unsigned), or if <tt>name</tt> begins with "<tt>java.</tt>".
   * @see #loadClass(String, boolean)
   * @see #resolveClass(Class)
   * @see java.security.CodeSource
   * @see java.security.SecureClassLoader
   * @since 1.1
   */
  protected final Class<?> defineClass(String name, byte[] b, int off, int len)
      throws ClassFormatError {
    return defineClass(name, b, off, len, null);
  }

  /* Determine protection domain, and check that:
      - not define java.* class,
      - signer of this class matches signers for the rest of the classes in
        package.
  */
  private ProtectionDomain preDefineClass(String name,
      ProtectionDomain pd) {
    if (!checkName(name)) {
      throw new NoClassDefFoundError("IllegalName: " + name);
    }

    if ((name != null) && name.startsWith("java.")) {
      throw new SecurityException
          ("Prohibited package name: " +
              name.substring(0, name.lastIndexOf('.')));
    }
    if (pd == null) {
      pd = defaultDomain;
    }

    if (name != null) {
      checkCerts(name, pd.getCodeSource());
    }

    return pd;
  }

  private String defineClassSourceLocation(ProtectionDomain pd) {
    CodeSource cs = pd.getCodeSource();
    String source = null;
    if (cs != null && cs.getLocation() != null) {
      source = cs.getLocation().toString();
    }
    return source;
  }

  private void postDefineClass(Class<?> c, ProtectionDomain pd) {
    if (pd.getCodeSource() != null) {
      Certificate certs[] = pd.getCodeSource().getCertificates();
      if (certs != null) {
        setSigners(c, certs);
      }
    }
  }

  /**
   * Converts an array of bytes into an instance of class <tt>Class</tt>,
   * with an optional <tt>ProtectionDomain</tt>.  If the domain is
   * <tt>null</tt>, then a default domain will be assigned to the class as
   * specified in the documentation for {@link #defineClass(String, byte[],
   * int, int)}.  Before the class can be used it must be resolved.
   *
   * <p> The first class defined in a package determines the exact set of
   * certificates that all subsequent classes defined in that package must
   * contain.  The set of certificates for a class is obtained from the
   * {@link java.security.CodeSource <tt>CodeSource</tt>} within the
   * <tt>ProtectionDomain</tt> of the class.  Any classes added to that
   * package must contain the same set of certificates or a
   * <tt>SecurityException</tt> will be thrown.  Note that if
   * <tt>name</tt> is <tt>null</tt>, this check is not performed.
   * You should always pass in the <a href="#name">binary name</a> of the
   * class you are defining as well as the bytes.  This ensures that the
   * class you are defining is indeed the class you think it is.
   *
   * <p> The specified <tt>name</tt> cannot begin with "<tt>java.</tt>", since
   * all classes in the "<tt>java.*</tt> packages can only be defined by the
   * bootstrap class loader.  If <tt>name</tt> is not <tt>null</tt>, it
   * must be equal to the <a href="#name">binary name</a> of the class
   * specified by the byte array "<tt>b</tt>", otherwise a {@link
   * NoClassDefFoundError <tt>NoClassDefFoundError</tt>} will be thrown. </p>
   *
   * @param name The expected <a href="#name">binary name</a> of the class, or <tt>null</tt> if not
   * known
   * @param b The bytes that make up the class data. The bytes in positions <tt>off</tt> through
   * <tt>off+len-1</tt> should have the format of a valid class file as defined by <cite>The
   * Java&trade; Virtual Machine Specification</cite>.
   * @param off The start offset in <tt>b</tt> of the class data
   * @param len The length of the class data
   * @param protectionDomain The ProtectionDomain of the class
   * @return The <tt>Class</tt> object created from the data, and optional
   * <tt>ProtectionDomain</tt>.
   * @throws ClassFormatError If the data did not contain a valid class
   * @throws NoClassDefFoundError If <tt>name</tt> is not equal to the <a href="#name">binary
   * name</a> of the class specified by <tt>b</tt>
   * @throws IndexOutOfBoundsException If either <tt>off</tt> or <tt>len</tt> is negative, or if
   * <tt>off+len</tt> is greater than <tt>b.length</tt>.
   * @throws SecurityException If an attempt is made to add this class to a package that contains
   * classes that were signed by a different set of certificates than this class, or if
   * <tt>name</tt> begins with "<tt>java.</tt>".
   */
  protected final Class<?> defineClass(String name, byte[] b, int off, int len,
      ProtectionDomain protectionDomain)
      throws ClassFormatError {
    protectionDomain = preDefineClass(name, protectionDomain);
    String source = defineClassSourceLocation(protectionDomain);
    Class<?> c = defineClass1(name, b, off, len, protectionDomain, source);
    postDefineClass(c, protectionDomain);
    return c;
  }

  /**
   * Converts a {@link java.nio.ByteBuffer <tt>ByteBuffer</tt>}
   * into an instance of class <tt>Class</tt>,
   * with an optional <tt>ProtectionDomain</tt>.  If the domain is
   * <tt>null</tt>, then a default domain will be assigned to the class as
   * specified in the documentation for {@link #defineClass(String, byte[],
   * int, int)}.  Before the class can be used it must be resolved.
   *
   * <p>The rules about the first class defined in a package determining the
   * set of certificates for the package, and the restrictions on class names
   * are identical to those specified in the documentation for {@link
   * #defineClass(String, byte[], int, int, ProtectionDomain)}.
   *
   * <p> An invocation of this method of the form
   * <i>cl</i><tt>.defineClass(</tt><i>name</i><tt>,</tt>
   * <i>bBuffer</i><tt>,</tt> <i>pd</i><tt>)</tt> yields exactly the same
   * result as the statements
   *
   * <p> <tt>
   * ...<br>
   * byte[] temp = new byte[bBuffer.{@link
   * java.nio.ByteBuffer#remaining remaining}()];<br>
   * bBuffer.{@link java.nio.ByteBuffer#get(byte[])
   * get}(temp);<br>
   * return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
   * cl.defineClass}(name, temp, 0,
   * temp.length, pd);<br>
   * </tt></p>
   *
   * @param name The expected <a href="#name">binary name</a>. of the class, or <tt>null</tt> if not
   * known
   * @param b The bytes that make up the class data. The bytes from positions <tt>b.position()</tt>
   * through <tt>b.position() + b.limit() -1 </tt> should have the format of a valid class file as
   * defined by <cite>The Java&trade; Virtual Machine Specification</cite>.
   * @param protectionDomain The ProtectionDomain of the class, or <tt>null</tt>.
   * @return The <tt>Class</tt> object created from the data, and optional
   * <tt>ProtectionDomain</tt>.
   * @throws ClassFormatError If the data did not contain a valid class.
   * @throws NoClassDefFoundError If <tt>name</tt> is not equal to the <a href="#name">binary
   * name</a> of the class specified by <tt>b</tt>
   * @throws SecurityException If an attempt is made to add this class to a package that contains
   * classes that were signed by a different set of certificates than this class, or if
   * <tt>name</tt> begins with "<tt>java.</tt>".
   * @see #defineClass(String, byte[], int, int, ProtectionDomain)
   * @since 1.5
   */
  protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
      ProtectionDomain protectionDomain)
      throws ClassFormatError {
    int len = b.remaining();

    // Use byte[] if not a direct ByteBufer:
    if (!b.isDirect()) {
      if (b.hasArray()) {
        return defineClass(name, b.array(),
            b.position() + b.arrayOffset(), len,
            protectionDomain);
      } else {
        // no array, or read-only array
        byte[] tb = new byte[len];
        b.get(tb);  // get bytes out of byte buffer.
        return defineClass(name, tb, 0, len, protectionDomain);
      }
    }

    protectionDomain = preDefineClass(name, protectionDomain);
    String source = defineClassSourceLocation(protectionDomain);
    Class<?> c = defineClass2(name, b, b.position(), len, protectionDomain, source);
    postDefineClass(c, protectionDomain);
    return c;
  }

  private native Class<?> defineClass0(String name, byte[] b, int off, int len,
      ProtectionDomain pd);

  private native Class<?> defineClass1(String name, byte[] b, int off, int len,
      ProtectionDomain pd, String source);

  private native Class<?> defineClass2(String name, java.nio.ByteBuffer b,
      int off, int len, ProtectionDomain pd,
      String source);

  // true if the name is null or has the potential to be a valid binary name
  private boolean checkName(String name) {
    if ((name == null) || (name.length() == 0)) {
      return true;
    }
    if ((name.indexOf('/') != -1)
        || (!VM.allowArraySyntax() && (name.charAt(0) == '['))) {
      return false;
    }
    return true;
  }

  private void checkCerts(String name, CodeSource cs) {
    int i = name.lastIndexOf('.');
    String pname = (i == -1) ? "" : name.substring(0, i);

    Certificate[] certs = null;
    if (cs != null) {
      certs = cs.getCertificates();
    }
    Certificate[] pcerts = null;
    if (parallelLockMap == null) {
      synchronized (this) {
        pcerts = package2certs.get(pname);
        if (pcerts == null) {
          package2certs.put(pname, (certs == null ? nocerts : certs));
        }
      }
    } else {
      pcerts = ((ConcurrentHashMap<String, Certificate[]>) package2certs).
          putIfAbsent(pname, (certs == null ? nocerts : certs));
    }
    if (pcerts != null && !compareCerts(pcerts, certs)) {
      throw new SecurityException("class \"" + name +
          "\"'s signer information does not match signer information of other classes in the same package");
    }
  }

  /**
   * check to make sure the certs for the new class (certs) are the same as
   * the certs for the first class inserted in the package (pcerts)
   */
  private boolean compareCerts(Certificate[] pcerts,
      Certificate[] certs) {
    // certs can be null, indicating no certs.
    if ((certs == null) || (certs.length == 0)) {
      return pcerts.length == 0;
    }

    // the length must be the same at this point
    if (certs.length != pcerts.length) {
      return false;
    }

    // go through and make sure all the certs in one array
    // are in the other and vice-versa.
    boolean match;
    for (int i = 0; i < certs.length; i++) {
      match = false;
      for (int j = 0; j < pcerts.length; j++) {
        if (certs[i].equals(pcerts[j])) {
          match = true;
          break;
        }
      }
      if (!match) {
        return false;
      }
    }

    // now do the same for pcerts
    for (int i = 0; i < pcerts.length; i++) {
      match = false;
      for (int j = 0; j < certs.length; j++) {
        if (pcerts[i].equals(certs[j])) {
          match = true;
          break;
        }
      }
      if (!match) {
        return false;
      }
    }

    return true;
  }

  /**
   * Links the specified class.  This (misleadingly named) method may be
   * used by a class loader to link a class.  If the class <tt>c</tt> has
   * already been linked, then this method simply returns. Otherwise, the
   * class is linked as described in the "Execution" chapter of
   * <cite>The Java&trade; Language Specification</cite>.
   *
   * @param c The class to link
   * @throws NullPointerException If <tt>c</tt> is <tt>null</tt>.
   * @see #defineClass(String, byte[], int, int)
   */
  protected final void resolveClass(Class<?> c) {
    resolveClass0(c);
  }

  private native void resolveClass0(Class<?> c);

  /**
   * Finds a class with the specified <a href="#name">binary name</a>,
   * loading it if necessary.
   *
   * <p> This method loads the class through the system class loader (see
   * {@link #getSystemClassLoader()}).  The <tt>Class</tt> object returned
   * might have more than one <tt>ClassLoader</tt> associated with it.
   * Subclasses of <tt>ClassLoader</tt> need not usually invoke this method,
   * because most class loaders need to override just {@link
   * #findClass(String)}.  </p>
   *
   * @param name The <a href="#name">binary name</a> of the class
   * @return The <tt>Class</tt> object for the specified <tt>name</tt>
   * @throws ClassNotFoundException If the class could not be found
   * @see #ClassLoader(ClassLoader)
   * @see #getParent()
   */
  protected final Class<?> findSystemClass(String name)
      throws ClassNotFoundException {
    ClassLoader system = getSystemClassLoader();
    if (system == null) {
      if (!checkName(name)) {
        throw new ClassNotFoundException(name);
      }
      Class<?> cls = findBootstrapClass(name);
      if (cls == null) {
        throw new ClassNotFoundException(name);
      }
      return cls;
    }
    return system.loadClass(name);
  }

  /**
   * Returns a class loaded by the bootstrap class loader;
   * or return null if not found.
   */
  private Class<?> findBootstrapClassOrNull(String name) {
    if (!checkName(name)) {
      return null;
    }

    return findBootstrapClass(name);
  }

  // return null if not found
  private native Class<?> findBootstrapClass(String name);

  /**
   * Returns the class with the given <a href="#name">binary name</a> if this
   * loader has been recorded by the Java virtual machine as an initiating
   * loader of a class with that <a href="#name">binary name</a>.  Otherwise
   * <tt>null</tt> is returned.
   *
   * @param name The <a href="#name">binary name</a> of the class
   * @return The <tt>Class</tt> object, or <tt>null</tt> if the class has not been loaded
   * @since 1.1
   */
  protected final Class<?> findLoadedClass(String name) {
    if (!checkName(name)) {
      return null;
    }
    return findLoadedClass0(name);
  }

  private native final Class<?> findLoadedClass0(String name);

  /**
   * Sets the signers of a class.  This should be invoked after defining a
   * class.
   *
   * @param c The <tt>Class</tt> object
   * @param signers The signers for the class
   * @since 1.1
   */
  protected final void setSigners(Class<?> c, Object[] signers) {
    c.setSigners(signers);
  }

  // -- Resource --

  /**
   * Finds the resource with the given name.  A resource is some data
   * (images, audio, text, etc) that can be accessed by class code in a way
   * that is independent of the location of the code.
   *
   * <p> The name of a resource is a '<tt>/</tt>'-separated path name that
   * identifies the resource.
   *
   * <p> This method will first search the parent class loader for the
   * resource; if the parent is <tt>null</tt> the path of the class loader
   * built-in to the virtual machine is searched.  That failing, this method
   * will invoke {@link #findResource(String)} to find the resource.  </p>
   *
   * @param name The resource name
   * @return A <tt>URL</tt> object for reading the resource, or <tt>null</tt> if the resource could
   * not be found or the invoker doesn't have adequate  privileges to get the resource.
   * @apiNote When overriding this method it is recommended that an implementation ensures that any
   * delegation is consistent with the {@link #getResources(java.lang.String) getResources(String)}
   * method.
   * @since 1.1
   */
  public URL getResource(String name) {
    URL url;
    if (parent != null) {
      url = parent.getResource(name);
    } else {
      url = getBootstrapResource(name);
    }
    if (url == null) {
      url = findResource(name);
    }
    return url;
  }

  /**
   * Finds all the resources with the given name. A resource is some data
   * (images, audio, text, etc) that can be accessed by class code in a way
   * that is independent of the location of the code.
   *
   * <p>The name of a resource is a <tt>/</tt>-separated path name that
   * identifies the resource.
   *
   * <p> The search order is described in the documentation for {@link
   * #getResource(String)}.  </p>
   *
   * @param name The resource name
   * @return An enumeration of {@link java.net.URL <tt>URL</tt>} objects for the resource.  If no
   * resources could  be found, the enumeration will be empty.  Resources that the class loader
   * doesn't have access to will not be in the enumeration.
   * @throws IOException If I/O errors occur
   * @apiNote When overriding this method it is recommended that an implementation ensures that any
   * delegation is consistent with the {@link #getResource(java.lang.String) getResource(String)}
   * method. This should ensure that the first element returned by the Enumeration's {@code
   * nextElement} method is the same resource that the {@code getResource(String)} method would
   * return.
   * @see #findResources(String)
   * @since 1.2
   */
  public Enumeration<URL> getResources(String name) throws IOException {
    @SuppressWarnings("unchecked")
    Enumeration<URL>[] tmp = (Enumeration<URL>[]) new Enumeration<?>[2];
    if (parent != null) {
      tmp[0] = parent.getResources(name);
    } else {
      tmp[0] = getBootstrapResources(name);
    }
    tmp[1] = findResources(name);

    return new CompoundEnumeration<>(tmp);
  }

  /**
   * Finds the resource with the given name. Class loader implementations
   * should override this method to specify where to find resources.
   *
   * @param name The resource name
   * @return A <tt>URL</tt> object for reading the resource, or <tt>null</tt> if the resource could
   * not be found
   * @since 1.2
   */
  protected URL findResource(String name) {
    return null;
  }

  /**
   * Returns an enumeration of {@link java.net.URL <tt>URL</tt>} objects
   * representing all the resources with the given name. Class loader
   * implementations should override this method to specify where to load
   * resources from.
   *
   * @param name The resource name
   * @return An enumeration of {@link java.net.URL <tt>URL</tt>} objects for the resources
   * @throws IOException If I/O errors occur
   * @since 1.2
   */
  protected Enumeration<URL> findResources(String name) throws IOException {
    return java.util.Collections.emptyEnumeration();
  }

  /**
   * Registers the caller as parallel capable.
   * The registration succeeds if and only if all of the following
   * conditions are met:
   * <ol>
   * <li> no instance of the caller has been created</li>
   * <li> all of the super classes (except class Object) of the caller are
   * registered as parallel capable</li>
   * </ol>
   * <p>Note that once a class loader is registered as parallel capable, there
   * is no way to change it back.</p>
   *
   * @return true if the caller is successfully registered as parallel capable and false if
   * otherwise.
   * @since 1.7
   */
  @CallerSensitive
  protected static boolean registerAsParallelCapable() {
    Class<? extends ClassLoader> callerClass =
        Reflection.getCallerClass().asSubclass(ClassLoader.class);
    return ParallelLoaders.register(callerClass);
  }

  /**
   * Find a resource of the specified name from the search path used to load
   * classes.  This method locates the resource through the system class
   * loader (see {@link #getSystemClassLoader()}).
   *
   * @param name The resource name
   * @return A {@link java.net.URL <tt>URL</tt>} object for reading the resource, or <tt>null</tt>
   * if the resource could not be found
   * @since 1.1
   */
  public static URL getSystemResource(String name) {
    ClassLoader system = getSystemClassLoader();
    if (system == null) {
      return getBootstrapResource(name);
    }
    return system.getResource(name);
  }

  /**
   * Finds all resources of the specified name from the search path used to
   * load classes.  The resources thus found are returned as an
   * {@link java.util.Enumeration <tt>Enumeration</tt>} of {@link
   * java.net.URL <tt>URL</tt>} objects.
   *
   * <p> The search order is described in the documentation for {@link
   * #getSystemResource(String)}.  </p>
   *
   * @param name The resource name
   * @return An enumeration of resource {@link java.net.URL <tt>URL</tt>} objects
   * @throws IOException If I/O errors occur
   * @since 1.2
   */
  public static Enumeration<URL> getSystemResources(String name)
      throws IOException {
    ClassLoader system = getSystemClassLoader();
    if (system == null) {
      return getBootstrapResources(name);
    }
    return system.getResources(name);
  }

  /**
   * Find resources from the VM's built-in classloader.
   */
  private static URL getBootstrapResource(String name) {
    URLClassPath ucp = getBootstrapClassPath();
    Resource res = ucp.getResource(name);
    return res != null ? res.getURL() : null;
  }

  /**
   * Find resources from the VM's built-in classloader.
   */
  private static Enumeration<URL> getBootstrapResources(String name)
      throws IOException {
    final Enumeration<Resource> e =
        getBootstrapClassPath().getResources(name);
    return new Enumeration<URL>() {
      public URL nextElement() {
        return e.nextElement().getURL();
      }

      public boolean hasMoreElements() {
        return e.hasMoreElements();
      }
    };
  }

  // Returns the URLClassPath that is used for finding system resources.
  static URLClassPath getBootstrapClassPath() {
    return sun.misc.Launcher.getBootstrapClassPath();
  }


  /**
   * Returns an input stream for reading the specified resource.
   *
   * <p> The search order is described in the documentation for {@link
   * #getResource(String)}.  </p>
   *
   * @param name The resource name
   * @return An input stream for reading the resource, or <tt>null</tt> if the resource could not be
   * found
   * @since 1.1
   */
  public InputStream getResourceAsStream(String name) {
    URL url = getResource(name);
    try {
      return url != null ? url.openStream() : null;
    } catch (IOException e) {
      return null;
    }
  }

  /**
   * Open for reading, a resource of the specified name from the search path
   * used to load classes.  This method locates the resource through the
   * system class loader (see {@link #getSystemClassLoader()}).
   *
   * @param name The resource name
   * @return An input stream for reading the resource, or <tt>null</tt> if the resource could not be
   * found
   * @since 1.1
   */
  public static InputStream getSystemResourceAsStream(String name) {
    URL url = getSystemResource(name);
    try {
      return url != null ? url.openStream() : null;
    } catch (IOException e) {
      return null;
    }
  }

  // -- Hierarchy --

  /**
   * Returns the parent class loader for delegation. Some implementations may
   * use <tt>null</tt> to represent the bootstrap class loader. This method
   * will return <tt>null</tt> in such implementations if this class loader's
   * parent is the bootstrap class loader.
   *
   * <p> If a security manager is present, and the invoker's class loader is
   * not <tt>null</tt> and is not an ancestor of this class loader, then this
   * method invokes the security manager's {@link
   * SecurityManager#checkPermission(java.security.Permission)
   * <tt>checkPermission</tt>} method with a {@link
   * RuntimePermission#RuntimePermission(String)
   * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
   * access to the parent class loader is permitted.  If not, a
   * <tt>SecurityException</tt> will be thrown.  </p>
   *
   * @return The parent <tt>ClassLoader</tt>
   * @throws SecurityException If a security manager exists and its <tt>checkPermission</tt> method
   * doesn't allow access to this class loader's parent class loader.
   * @since 1.2
   */
  @CallerSensitive
  public final ClassLoader getParent() {
    if (parent == null) {
      return null;
    }
    SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
      // Check access to the parent class loader
      // If the caller's class loader is same as this class loader,
      // permission check is performed.
      checkClassLoaderPermission(parent, Reflection.getCallerClass());
    }
    return parent;
  }

  /**
   * Returns the system class loader for delegation.  This is the default
   * delegation parent for new <tt>ClassLoader</tt> instances, and is
   * typically the class loader used to start the application.
   *
   * <p> This method is first invoked early in the runtime's startup
   * sequence, at which point it creates the system class loader and sets it
   * as the context class loader of the invoking <tt>Thread</tt>.
   *
   * <p> The default system class loader is an implementation-dependent
   * instance of this class.
   *
   * <p> If the system property "<tt>java.system.class.loader</tt>" is defined
   * when this method is first invoked then the value of that property is
   * taken to be the name of a class that will be returned as the system
   * class loader.  The class is loaded using the default system class loader
   * and must define a public constructor that takes a single parameter of
   * type <tt>ClassLoader</tt> which is used as the delegation parent.  An
   * instance is then created using this constructor with the default system
   * class loader as the parameter.  The resulting class loader is defined
   * to be the system class loader.
   *
   * <p> If a security manager is present, and the invoker's class loader is
   * not <tt>null</tt> and the invoker's class loader is not the same as or
   * an ancestor of the system class loader, then this method invokes the
   * security manager's {@link
   * SecurityManager#checkPermission(java.security.Permission)
   * <tt>checkPermission</tt>} method with a {@link
   * RuntimePermission#RuntimePermission(String)
   * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
   * access to the system class loader.  If not, a
   * <tt>SecurityException</tt> will be thrown.  </p>
   *
   * @return The system <tt>ClassLoader</tt> for delegation, or <tt>null</tt> if none
   * @throws SecurityException If a security manager exists and its <tt>checkPermission</tt> method
   * doesn't allow access to the system class loader.
   * @throws IllegalStateException If invoked recursively during the construction of the class
   * loader specified by the "<tt>java.system.class.loader</tt>" property.
   * @throws Error If the system property "<tt>java.system.class.loader</tt>" is defined but the
   * named class could not be loaded, the provider class does not define the required constructor,
   * or an exception is thrown by that constructor when it is invoked. The underlying cause of the
   * error can be retrieved via the {@link Throwable#getCause()} method.
   * @revised 1.4
   */
  @CallerSensitive
  public static ClassLoader getSystemClassLoader() {
    initSystemClassLoader();
    if (scl == null) {
      return null;
    }
    SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
      checkClassLoaderPermission(scl, Reflection.getCallerClass());
    }
    return scl;
  }

  private static synchronized void initSystemClassLoader() {
    if (!sclSet) {
      if (scl != null) {
        throw new IllegalStateException("recursive invocation");
      }
      sun.misc.Launcher l = sun.misc.Launcher.getLauncher();
      if (l != null) {
        Throwable oops = null;
        scl = l.getClassLoader();
        try {
          scl = AccessController.doPrivileged(
              new SystemClassLoaderAction(scl));
        } catch (PrivilegedActionException pae) {
          oops = pae.getCause();
          if (oops instanceof InvocationTargetException) {
            oops = oops.getCause();
          }
        }
        if (oops != null) {
          if (oops instanceof Error) {
            throw (Error) oops;
          } else {
            // wrap the exception
            throw new Error(oops);
          }
        }
      }
      sclSet = true;
    }
  }

  // Returns true if the specified class loader can be found in this class
  // loader's delegation chain.
  boolean isAncestor(ClassLoader cl) {
    ClassLoader acl = this;
    do {
      acl = acl.parent;
      if (cl == acl) {
        return true;
      }
    } while (acl != null);
    return false;
  }

  // Tests if class loader access requires "getClassLoader" permission
  // check.  A class loader 'from' can access class loader 'to' if
  // class loader 'from' is same as class loader 'to' or an ancestor
  // of 'to'.  The class loader in a system domain can access
  // any class loader.
  private static boolean needsClassLoaderPermissionCheck(ClassLoader from,
      ClassLoader to) {
    if (from == to) {
      return false;
    }

    if (from == null) {
      return false;
    }

    return !to.isAncestor(from);
  }

  // Returns the class's class loader, or null if none.
  static ClassLoader getClassLoader(Class<?> caller) {
    // This can be null if the VM is requesting it
    if (caller == null) {
      return null;
    }
    // Circumvent security check since this is package-private
    return caller.getClassLoader0();
  }

  /*
   * Checks RuntimePermission("getClassLoader") permission
   * if caller's class loader is not null and caller's class loader
   * is not the same as or an ancestor of the given cl argument.
   */
  static void checkClassLoaderPermission(ClassLoader cl, Class<?> caller) {
    SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
      // caller can be null if the VM is requesting it
      ClassLoader ccl = getClassLoader(caller);
      if (needsClassLoaderPermissionCheck(ccl, cl)) {
        sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
      }
    }
  }

  // The class loader for the system
  // @GuardedBy("ClassLoader.class")
  private static ClassLoader scl;

  // Set to true once the system class loader has been set
  // @GuardedBy("ClassLoader.class")
  private static boolean sclSet;

  // -- Package --

  /**
   * Defines a package by name in this <tt>ClassLoader</tt>.  This allows
   * class loaders to define the packages for their classes. Packages must
   * be created before the class is defined, and package names must be
   * unique within a class loader and cannot be redefined or changed once
   * created.
   *
   * @param name The package name
   * @param specTitle The specification title
   * @param specVersion The specification version
   * @param specVendor The specification vendor
   * @param implTitle The implementation title
   * @param implVersion The implementation version
   * @param implVendor The implementation vendor
   * @param sealBase If not <tt>null</tt>, then this package is sealed with respect to the given
   * code source {@link java.net.URL <tt>URL</tt>}  object.  Otherwise, the package is not sealed.
   * @return The newly defined <tt>Package</tt> object
   * @throws IllegalArgumentException If package name duplicates an existing package either in this
   * class loader or one of its ancestors
   * @since 1.2
   */
  protected Package definePackage(String name, String specTitle,
      String specVersion, String specVendor,
      String implTitle, String implVersion,
      String implVendor, URL sealBase)
      throws IllegalArgumentException {
    synchronized (packages) {
      Package pkg = getPackage(name);
      if (pkg != null) {
        throw new IllegalArgumentException(name);
      }
      pkg = new Package(name, specTitle, specVersion, specVendor,
          implTitle, implVersion, implVendor,
          sealBase, this);
      packages.put(name, pkg);
      return pkg;
    }
  }

  /**
   * Returns a <tt>Package</tt> that has been defined by this class loader
   * or any of its ancestors.
   *
   * @param name The package name
   * @return The <tt>Package</tt> corresponding to the given name, or <tt>null</tt> if not found
   * @since 1.2
   */
  protected Package getPackage(String name) {
    Package pkg;
    synchronized (packages) {
      pkg = packages.get(name);
    }
    if (pkg == null) {
      if (parent != null) {
        pkg = parent.getPackage(name);
      } else {
        pkg = Package.getSystemPackage(name);
      }
      if (pkg != null) {
        synchronized (packages) {
          Package pkg2 = packages.get(name);
          if (pkg2 == null) {
            packages.put(name, pkg);
          } else {
            pkg = pkg2;
          }
        }
      }
    }
    return pkg;
  }

  /**
   * Returns all of the <tt>Packages</tt> defined by this class loader and
   * its ancestors.
   *
   * @return The array of <tt>Package</tt> objects defined by this <tt>ClassLoader</tt>
   * @since 1.2
   */
  protected Package[] getPackages() {
    Map<String, Package> map;
    synchronized (packages) {
      map = new HashMap<>(packages);
    }
    Package[] pkgs;
    if (parent != null) {
      pkgs = parent.getPackages();
    } else {
      pkgs = Package.getSystemPackages();
    }
    if (pkgs != null) {
      for (int i = 0; i < pkgs.length; i++) {
        String pkgName = pkgs[i].getName();
        if (map.get(pkgName) == null) {
          map.put(pkgName, pkgs[i]);
        }
      }
    }
    return map.values().toArray(new Package[map.size()]);
  }

  // -- Native library access --

  /**
   * Returns the absolute path name of a native library.  The VM invokes this
   * method to locate the native libraries that belong to classes loaded with
   * this class loader. If this method returns <tt>null</tt>, the VM
   * searches the library along the path specified as the
   * "<tt>java.library.path</tt>" property.
   *
   * @param libname The library name
   * @return The absolute path of the native library
   * @see System#loadLibrary(String)
   * @see System#mapLibraryName(String)
   * @since 1.2
   */
  protected String findLibrary(String libname) {
    return null;
  }

  /**
   * The inner class NativeLibrary denotes a loaded native library instance.
   * Every classloader contains a vector of loaded native libraries in the
   * private field <tt>nativeLibraries</tt>.  The native libraries loaded
   * into the system are entered into the <tt>systemNativeLibraries</tt>
   * vector.
   *
   * <p> Every native library requires a particular version of JNI. This is
   * denoted by the private <tt>jniVersion</tt> field.  This field is set by
   * the VM when it loads the library, and used by the VM to pass the correct
   * version of JNI to the native methods.  </p>
   *
   * @see ClassLoader
   * @since 1.2
   */
  static class NativeLibrary {

    // opaque handle to native library, used in native code.
    long handle;
    // the version of JNI environment the native library requires.
    private int jniVersion;
    // the class from which the library is loaded, also indicates
    // the loader this native library belongs.
    private final Class<?> fromClass;
    // the canonicalized name of the native library.
    // or static library name
    String name;
    // Indicates if the native library is linked into the VM
    boolean isBuiltin;
    // Indicates if the native library is loaded
    boolean loaded;

    native void load(String name, boolean isBuiltin);

    native long find(String name);

    native void unload(String name, boolean isBuiltin);

    public NativeLibrary(Class<?> fromClass, String name, boolean isBuiltin) {
      this.name = name;
      this.fromClass = fromClass;
      this.isBuiltin = isBuiltin;
    }

    protected void finalize() {
      synchronized (loadedLibraryNames) {
        if (fromClass.getClassLoader() != null && loaded) {
                    /* remove the native library name */
          int size = loadedLibraryNames.size();
          for (int i = 0; i < size; i++) {
            if (name.equals(loadedLibraryNames.elementAt(i))) {
              loadedLibraryNames.removeElementAt(i);
              break;
            }
          }
                    /* unload the library. */
          ClassLoader.nativeLibraryContext.push(this);
          try {
            unload(name, isBuiltin);
          } finally {
            ClassLoader.nativeLibraryContext.pop();
          }
        }
      }
    }

    // Invoked in the VM to determine the context class in
    // JNI_Load/JNI_Unload
    static Class<?> getFromClass() {
      return ClassLoader.nativeLibraryContext.peek().fromClass;
    }
  }

  // All native library names we've loaded.
  private static Vector<String> loadedLibraryNames = new Vector<>();

  // Native libraries belonging to system classes.
  private static Vector<NativeLibrary> systemNativeLibraries
      = new Vector<>();

  // Native libraries associated with the class loader.
  private Vector<NativeLibrary> nativeLibraries = new Vector<>();

  // native libraries being loaded/unloaded.
  private static Stack<NativeLibrary> nativeLibraryContext = new Stack<>();

  // The paths searched for libraries
  private static String usr_paths[];
  private static String sys_paths[];

  private static String[] initializePath(String propname) {
    String ldpath = System.getProperty(propname, "");
    String ps = File.pathSeparator;
    int ldlen = ldpath.length();
    int i, j, n;
    // Count the separators in the path
    i = ldpath.indexOf(ps);
    n = 0;
    while (i >= 0) {
      n++;
      i = ldpath.indexOf(ps, i + 1);
    }

    // allocate the array of paths - n :'s = n + 1 path elements
    String[] paths = new String[n + 1];

    // Fill the array with paths from the ldpath
    n = i = 0;
    j = ldpath.indexOf(ps);
    while (j >= 0) {
      if (j - i > 0) {
        paths[n++] = ldpath.substring(i, j);
      } else if (j - i == 0) {
        paths[n++] = ".";
      }
      i = j + 1;
      j = ldpath.indexOf(ps, i);
    }
    paths[n] = ldpath.substring(i, ldlen);
    return paths;
  }

  // Invoked in the java.lang.Runtime class to implement load and loadLibrary.
  static void loadLibrary(Class<?> fromClass, String name,
      boolean isAbsolute) {
    ClassLoader loader =
        (fromClass == null) ? null : fromClass.getClassLoader();
    if (sys_paths == null) {
      usr_paths = initializePath("java.library.path");
      sys_paths = initializePath("sun.boot.library.path");
    }
    if (isAbsolute) {
      if (loadLibrary0(fromClass, new File(name))) {
        return;
      }
      throw new UnsatisfiedLinkError("Can't load library: " + name);
    }
    if (loader != null) {
      String libfilename = loader.findLibrary(name);
      if (libfilename != null) {
        File libfile = new File(libfilename);
        if (!libfile.isAbsolute()) {
          throw new UnsatisfiedLinkError(
              "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
        }
        if (loadLibrary0(fromClass, libfile)) {
          return;
        }
        throw new UnsatisfiedLinkError("Can't load " + libfilename);
      }
    }
    for (int i = 0; i < sys_paths.length; i++) {
      File libfile = new File(sys_paths[i], System.mapLibraryName(name));
      if (loadLibrary0(fromClass, libfile)) {
        return;
      }
      libfile = ClassLoaderHelper.mapAlternativeName(libfile);
      if (libfile != null && loadLibrary0(fromClass, libfile)) {
        return;
      }
    }
    if (loader != null) {
      for (int i = 0; i < usr_paths.length; i++) {
        File libfile = new File(usr_paths[i],
            System.mapLibraryName(name));
        if (loadLibrary0(fromClass, libfile)) {
          return;
        }
        libfile = ClassLoaderHelper.mapAlternativeName(libfile);
        if (libfile != null && loadLibrary0(fromClass, libfile)) {
          return;
        }
      }
    }
    // Oops, it failed
    throw new UnsatisfiedLinkError("no " + name + " in java.library.path");
  }

  private static native String findBuiltinLib(String name);

  private static boolean loadLibrary0(Class<?> fromClass, final File file) {
    // Check to see if we're attempting to access a static library
    String name = findBuiltinLib(file.getName());
    boolean isBuiltin = (name != null);
    if (!isBuiltin) {
      boolean exists = AccessController.doPrivileged(
          new PrivilegedAction<Object>() {
            public Object run() {
              return file.exists() ? Boolean.TRUE : null;
            }
          })
          != null;
      if (!exists) {
        return false;
      }
      try {
        name = file.getCanonicalPath();
      } catch (IOException e) {
        return false;
      }
    }
    ClassLoader loader =
        (fromClass == null) ? null : fromClass.getClassLoader();
    Vector<NativeLibrary> libs =
        loader != null ? loader.nativeLibraries : systemNativeLibraries;
    synchronized (libs) {
      int size = libs.size();
      for (int i = 0; i < size; i++) {
        NativeLibrary lib = libs.elementAt(i);
        if (name.equals(lib.name)) {
          return true;
        }
      }

      synchronized (loadedLibraryNames) {
        if (loadedLibraryNames.contains(name)) {
          throw new UnsatisfiedLinkError
              ("Native Library " +
                  name +
                  " already loaded in another classloader");
        }
                /* If the library is being loaded (must be by the same thread,
                 * because Runtime.load and Runtime.loadLibrary are
                 * synchronous). The reason is can occur is that the JNI_OnLoad
                 * function can cause another loadLibrary invocation.
                 *
                 * Thus we can use a static stack to hold the list of libraries
                 * we are loading.
                 *
                 * If there is a pending load operation for the library, we
                 * immediately return success; otherwise, we raise
                 * UnsatisfiedLinkError.
                 */
        int n = nativeLibraryContext.size();
        for (int i = 0; i < n; i++) {
          NativeLibrary lib = nativeLibraryContext.elementAt(i);
          if (name.equals(lib.name)) {
            if (loader == lib.fromClass.getClassLoader()) {
              return true;
            } else {
              throw new UnsatisfiedLinkError
                  ("Native Library " +
                      name +
                      " is being loaded in another classloader");
            }
          }
        }
        NativeLibrary lib = new NativeLibrary(fromClass, name, isBuiltin);
        nativeLibraryContext.push(lib);
        try {
          lib.load(name, isBuiltin);
        } finally {
          nativeLibraryContext.pop();
        }
        if (lib.loaded) {
          loadedLibraryNames.addElement(name);
          libs.addElement(lib);
          return true;
        }
        return false;
      }
    }
  }

  // Invoked in the VM class linking code.
  static long findNative(ClassLoader loader, String name) {
    Vector<NativeLibrary> libs =
        loader != null ? loader.nativeLibraries : systemNativeLibraries;
    synchronized (libs) {
      int size = libs.size();
      for (int i = 0; i < size; i++) {
        NativeLibrary lib = libs.elementAt(i);
        long entry = lib.find(name);
        if (entry != 0) {
          return entry;
        }
      }
    }
    return 0;
  }

  // -- Assertion management --

  final Object assertionLock;

  // The default toggle for assertion checking.
  // @GuardedBy("assertionLock")
  private boolean defaultAssertionStatus = false;

  // Maps String packageName to Boolean package default assertion status Note
  // that the default package is placed under a null map key.  If this field
  // is null then we are delegating assertion status queries to the VM, i.e.,
  // none of this ClassLoader's assertion status modification methods have
  // been invoked.
  // @GuardedBy("assertionLock")
  private Map<String, Boolean> packageAssertionStatus = null;

  // Maps String fullyQualifiedClassName to Boolean assertionStatus If this
  // field is null then we are delegating assertion status queries to the VM,
  // i.e., none of this ClassLoader's assertion status modification methods
  // have been invoked.
  // @GuardedBy("assertionLock")
  Map<String, Boolean> classAssertionStatus = null;

  /**
   * Sets the default assertion status for this class loader.  This setting
   * determines whether classes loaded by this class loader and initialized
   * in the future will have assertions enabled or disabled by default.
   * This setting may be overridden on a per-package or per-class basis by
   * invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
   * #setClassAssertionStatus(String, boolean)}.
   *
   * @param enabled <tt>true</tt> if classes loaded by this class loader will henceforth have
   * assertions enabled by default, <tt>false</tt> if they will have assertions disabled by
   * default.
   * @since 1.4
   */
  public void setDefaultAssertionStatus(boolean enabled) {
    synchronized (assertionLock) {
      if (classAssertionStatus == null) {
        initializeJavaAssertionMaps();
      }

      defaultAssertionStatus = enabled;
    }
  }

  /**
   * Sets the package default assertion status for the named package.  The
   * package default assertion status determines the assertion status for
   * classes initialized in the future that belong to the named package or
   * any of its "subpackages".
   *
   * <p> A subpackage of a package named p is any package whose name begins
   * with "<tt>p.</tt>".  For example, <tt>javax.swing.text</tt> is a
   * subpackage of <tt>javax.swing</tt>, and both <tt>java.util</tt> and
   * <tt>java.lang.reflect</tt> are subpackages of <tt>java</tt>.
   *
   * <p> In the event that multiple package defaults apply to a given class,
   * the package default pertaining to the most specific package takes
   * precedence over the others.  For example, if <tt>javax.lang</tt> and
   * <tt>javax.lang.reflect</tt> both have package defaults associated with
   * them, the latter package default applies to classes in
   * <tt>javax.lang.reflect</tt>.
   *
   * <p> Package defaults take precedence over the class loader's default
   * assertion status, and may be overridden on a per-class basis by invoking
   * {@link #setClassAssertionStatus(String, boolean)}.  </p>
   *
   * @param packageName The name of the package whose package default assertion status is to be set.
   * A <tt>null</tt> value indicates the unnamed package that is "current" (see section 7.4.2 of
   * <cite>The Java&trade; Language Specification</cite>.)
   * @param enabled <tt>true</tt> if classes loaded by this classloader and belonging to the named
   * package or any of its subpackages will have assertions enabled by default, <tt>false</tt> if
   * they will have assertions disabled by default.
   * @since 1.4
   */
  public void setPackageAssertionStatus(String packageName,
      boolean enabled) {
    synchronized (assertionLock) {
      if (packageAssertionStatus == null) {
        initializeJavaAssertionMaps();
      }

      packageAssertionStatus.put(packageName, enabled);
    }
  }

  /**
   * Sets the desired assertion status for the named top-level class in this
   * class loader and any nested classes contained therein.  This setting
   * takes precedence over the class loader's default assertion status, and
   * over any applicable per-package default.  This method has no effect if
   * the named class has already been initialized.  (Once a class is
   * initialized, its assertion status cannot change.)
   *
   * <p> If the named class is not a top-level class, this invocation will
   * have no effect on the actual assertion status of any class. </p>
   *
   * @param className The fully qualified class name of the top-level class whose assertion status
   * is to be set.
   * @param enabled <tt>true</tt> if the named class is to have assertions enabled when (and if) it
   * is initialized, <tt>false</tt> if the class is to have assertions disabled.
   * @since 1.4
   */
  public void setClassAssertionStatus(String className, boolean enabled) {
    synchronized (assertionLock) {
      if (classAssertionStatus == null) {
        initializeJavaAssertionMaps();
      }

      classAssertionStatus.put(className, enabled);
    }
  }

  /**
   * Sets the default assertion status for this class loader to
   * <tt>false</tt> and discards any package defaults or class assertion
   * status settings associated with the class loader.  This method is
   * provided so that class loaders can be made to ignore any command line or
   * persistent assertion status settings and "start with a clean slate."
   *
   * @since 1.4
   */
  public void clearAssertionStatus() {
        /*
         * Whether or not "Java assertion maps" are initialized, set
         * them to empty maps, effectively ignoring any present settings.
         */
    synchronized (assertionLock) {
      classAssertionStatus = new HashMap<>();
      packageAssertionStatus = new HashMap<>();
      defaultAssertionStatus = false;
    }
  }

  /**
   * Returns the assertion status that would be assigned to the specified
   * class if it were to be initialized at the time this method is invoked.
   * If the named class has had its assertion status set, the most recent
   * setting will be returned; otherwise, if any package default assertion
   * status pertains to this class, the most recent setting for the most
   * specific pertinent package default assertion status is returned;
   * otherwise, this class loader's default assertion status is returned.
   * </p>
   *
   * @param className The fully qualified class name of the class whose desired assertion status is
   * being queried.
   * @return The desired assertion status of the specified class.
   * @see #setClassAssertionStatus(String, boolean)
   * @see #setPackageAssertionStatus(String, boolean)
   * @see #setDefaultAssertionStatus(boolean)
   * @since 1.4
   */
  boolean desiredAssertionStatus(String className) {
    synchronized (assertionLock) {
      // assert classAssertionStatus   != null;
      // assert packageAssertionStatus != null;

      // Check for a class entry
      Boolean result = classAssertionStatus.get(className);
      if (result != null) {
        return result.booleanValue();
      }

      // Check for most specific package entry
      int dotIndex = className.lastIndexOf(".");
      if (dotIndex < 0) { // default package
        result = packageAssertionStatus.get(null);
        if (result != null) {
          return result.booleanValue();
        }
      }
      while (dotIndex > 0) {
        className = className.substring(0, dotIndex);
        result = packageAssertionStatus.get(className);
        if (result != null) {
          return result.booleanValue();
        }
        dotIndex = className.lastIndexOf(".", dotIndex - 1);
      }

      // Return the classloader default
      return defaultAssertionStatus;
    }
  }

  // Set up the assertions with information provided by the VM.
  // Note: Should only be called inside a synchronized block
  private void initializeJavaAssertionMaps() {
    // assert Thread.holdsLock(assertionLock);

    classAssertionStatus = new HashMap<>();
    packageAssertionStatus = new HashMap<>();
    AssertionStatusDirectives directives = retrieveDirectives();

    for (int i = 0; i < directives.classes.length; i++) {
      classAssertionStatus.put(directives.classes[i],
          directives.classEnabled[i]);
    }

    for (int i = 0; i < directives.packages.length; i++) {
      packageAssertionStatus.put(directives.packages[i],
          directives.packageEnabled[i]);
    }

    defaultAssertionStatus = directives.deflt;
  }

  // Retrieves the assertion directives from the VM.
  private static native AssertionStatusDirectives retrieveDirectives();
}


class SystemClassLoaderAction
    implements PrivilegedExceptionAction<ClassLoader> {

  private ClassLoader parent;

  SystemClassLoaderAction(ClassLoader parent) {
    this.parent = parent;
  }

  public ClassLoader run() throws Exception {
    String cls = System.getProperty("java.system.class.loader");
    if (cls == null) {
      return parent;
    }

    Constructor<?> ctor = Class.forName(cls, true, parent)
        .getDeclaredConstructor(new Class<?>[]{ClassLoader.class});
    ClassLoader sys = (ClassLoader) ctor.newInstance(
        new Object[]{parent});
    Thread.currentThread().setContextClassLoader(sys);
    return sys;
  }
}
